This invention relates to an electric motor equipped with an apparatus for cooling a motor.
An electric motor referred to as a wheel motor is often used in arrangement with each of the wheels of a motorized vehicle such as a forklift or golf cart as means for driving the vehicle.
In a motorized vehicle, the wheels of the vehicle during travel move up and down due to unevenness in the surface of the road, and the wheels are turned to the left and right when the vehicle is steered. Consequently, when the aforementioned electric motor is disposed in operative association with each of the wheels, the arrangement must be such that the electric motor will not interfere with the corresponding wheel when the wheel undergoes the motions described. This means that there are space limitations as far as installation of the electric motor is concerned. Therefore, in order to install the electric motor in the limited space available, it is required that the electric motor be made as small as possible.
On the other hand, since a motorized vehicle is such that a comparatively heavy vehicle body must be moved, it is required that the output torque of the electric motor be considerably high.
In order to obtain an electric motor which is both compact and capable of delivering high output torque, a large current must be passed through the coil of the motor proper. However, passing a large current through the coil can cause the coil to heat up and eventually burn out. For this reason, it is required that the coil of the motor be cooled.
Conventionally, a cooling apparatus which performs such cooling is provided separately of the electric motor, and oil or air is used as the coolant. Accordingly, space must be separately provided in order to install the cooling apparatus. However, it is very difficult to provide additional space for accommodating the cooling apparatus where the space for installation of the electric motor is already limited, as in the aforementioned motorized vehicle. Furthermore, if it is attempted to force the cooling apparatus into the cramped space that is available, there is the danger that the cooling appparatus will interfere with the corresponding wheel when the wheel moves up and down as well as to the left and right. This means that a constraint must be placed upon movement of the wheel.
Thus, it is very difficult to provide both the electric motor and its cooling apparatus in a limited space. This has made it almost impossible to raise the output of a compact electric motor.
Further, in the prior art, the cooling apparatus is driven in concert with the electric motor. Hence, the cooling apparatus applies cooling to the motor coil even when the coil is not all that hot. This only wastes energy and results in inefficient cooling of the motor. Moreover, since a pump associated with the cooling apparatus is driven more than needed, the service life of the pump is curtailed.
Conventionally, the power fed to the motor and to a pump motor or fan motor in the cooling apparatus is supplied separately via a number of power supply lines from a power supply mounted on the vehicle frame. When the electric motor is used as a wheel motor, it is supported on the vehicle frame via a suspension or the like. However, since the suspension forms a relatively movable object which allows relative motion between the vehicle frame and the wheel motor, a number of electric lines such as the aforementioned complicated arrangement of power supply lines must be installed through the movable object. Thus disposing a number of electric lines through the movable object invites wire breakage and diminishes reliability.